DNA microarray hybridization is used to identify different viruses and viral strains. Hybridization with generic microchips (microarrays containing all possible hexameric oligonucleotides) can discrimination between point mutants quantify their contents in viral stocks. Comparison of hybridization patterns of vaccine strain and its neurovirulent revertant using a chip with 4096 elements identifies a few oligonucleotides, the binding of which is affected by the mutation. Quantification of fluorescence intensity of these elements can assess the relative abundance of the mutants. Another kind of oligonucleotide microchip containing probes specific for individual viruses and for groups of related viruses is used to identify viruses in biological samples and to classify them. This method was used to discriminate between different serotypes of rotaviruses, polioviruses, enteroviruses. It was also used to discriminate between SV40 (potential adventitious agent) and related human viruses BK and JC. Quantitative analysis of mutations in live viral vaccines was also performed. Ratio of two sub-strains of LeryLynn strain of live Mumps vaccine was measured. The results were presented at ASV meeting.